Embodiments of the invention relate generally to an arc elimination system and, more particularly, to plasma guns used in the arc elimination system.
Electrical circuits and switchgears have conductors separated by a dielectric material or gap of insulation such as air or gas. If the insulation between conductors or any other live parts such as an electrode, a metallic support or assembly connected to the conductor or the electrode is compromised, or voltage exceeds the insulation properties, an arc may occur between such conductors or live parts. The insulation between the live parts may become ionized, which makes the insulation conductive and enables formation of an arc flash.
Existing fuses and circuit breakers alone may not react fast enough to an arc flash to avoid any damage to personnel or equipment. An electric arc device such as an arc elimination system is used to short an electrical circuit and thus divert the electrical energy away from the accidental arc flash. The short circuit thus created is then cleared by tripping a fuse or circuit breaker. Electric arc devices are used in a variety of applications, including series capacitor protection, high power switches, acoustic generators, shock wave generators, and pulsed plasma thrusters, apart from the arc elimination systems. Such devices may include two or more main electrodes separated by a gap of air or gas.
Some known electric arc devices position main electrodes close to each other to provide an effective spread of ablative plasma from a plasma gun to the main electrodes due to shorter distance for the ablative plasma to spread from the plasma gun to the main electrodes. For medium voltage power systems, the distance or clearance between the main electrodes of the electric arc device may be reduced to, for example, about 50 to 75 millimeters (mm) from the recommended clearance of 150 mm. However, reducing the clearance between the main electrodes of the electric arc device too much may result in unwanted operation under system overvoltage conditions. Some existing electric arc devices implement a protection device such as a surge arrester to handle the overvoltage challenge associated with shorter clearance, and thus achieve the basic insulation level (BIL) as per the required standards. However, due to shorter clearance, contaminants or even the natural impedance of the air in the gap may result in undesirable arc formation between the main electrodes, which can lead to an unwanted operation of the electric arc device and also induce an undesired operation such as false tripping of a circuit breaker or fuse.
Therefore, some existing electric arc devices increase the clearance between the main electrodes to avoid such false tripping. However, these devices are typically less reliable due to the challenge posed by the longer clearances where the spreading of the ablative plasma may not be sufficient to reach all the main electrodes since the main electrodes are positioned at a greater distance apart from each other and also from the plasma gun.
Thus, there is a need to provide an arc elimination system and associated apparatuses that overcome some of the limitations described above.